1. Field of the Invention
The present invention relates to a leakage loss line type circularly-polarized wave antenna applied to wireless devices which provide users with wireless system services using circularly-polarized waves, such as satellite broadcast and satellite position information systems, and a high-frequency module or a wireless terminal into which is incorporated the same antenna. In particular, it relates to a small-size and thin leakage loss line type circularly-polarized wave antenna, suitable for providing users with information wireless system services using as a medium electromagnetic waves with long wavelengths compared with dimensions of the above wireless devices, and a high-frequency module including the antenna, and a wireless terminal into which are incorporated the antenna and the high-frequency module.
2. Description of the Related Art
Among various wireless systems, services using satellites have advantages of being capable of providing seamless services covering each country, having less screening effects of high-rise buildings because electromagnetic waves that serve as a medium arrive from substantially a zenith direction, etc. which are utilized for operating many systems such as seamless international calls, satellite broadcast, positioning systems, etc.
These systems can provide international seamless services, but have inevitably high possibilities of electromagnetic waves leaking to other countries or other regions. For this reason, in order to cope with such an electromagnetic wave leak problem, circularly-polarized waves are used to assign different polarized waves (right-handed and left-handed circularly-polarized waves) to adjacent countries or regions.
Right-handed circularly-polarized waves cannot be received by left-handed circularly-polarized wave antennas, and left-handed circularly-polarized waves cannot be received by right-handed circularly-polarized wave antennas. Also, linearly-polarized wave antennas can receive only a half of power of circularly-polarized waves.
For this reason, to provide users with wireless services using circularly-polarized electromagnetic waves efficiently, realization of a circularly-polarized wave antenna is important.
To realize a circularly-polarized wave antenna, 2 conventional methods are known, and widely practically used.
The first method is to position 2 linearly-polarized wave antennas perpendicularly to each other so that respective power feed phases of the antennas are shifted by 90 degrees. As this representative realized example, there is a famous cross dipole, which requires 2 power feed portions, and a means (e.g. a phase shifter) for shifting respective phases of the power feed portions by 90 degrees, which results in a large-scale circuit of a wireless device to which is applied an antenna, i.e., the problem with a size reduction of the same wireless device, as shown in Naohisa Goto, “ZUSETU ANTENNA”, IEICE, 1995, p. 219, for example.
The second method is to use an open-periphery patch antenna such as a micro-strip antenna, in which a circularly-polarized wave antenna is realized by 1 power feed point using a rectangular or circular two-dimensional patch which extends in two perpendicular axes. As shown in Misao Haneishi, “KOGATA HEIMEN ANTENNA”, IEICE, 1996, pp. 143-145, for example, by deforming a square or circular shape short on one side and long on the other respective to two perpendicular axes, one side of the square or half the perimeter of the circle is made different, so that the respective lengths are slightly longer or shorter than ½ of a wavelength of a radio wave to be received by an antenna, thereby shifting the respective power feed phases for these lengths by 90 degrees in one point power feed, as inductivity or capacitivity for the respective lengths perpendicular to each other respective to a power feed point.
This method has one power feed point compared to the first method, and therefore realizes a substantial scale reduction of a high-frequency circuit that feeds high-frequency power to the antenna, and is most practically used at present.
When this method is used, however, because it requires two-dimensionally ensuring antenna dimensions of substantially ½ of a wavelength of a radio wave to be received by an antenna (i.e., ensuring the area of the square having one side of substantially ½ of the wavelength), there is still the problem with the application to modern palm small-size terminals.
To reduce antenna dimensions in this method, by lining or covering an antenna with a dielectric having a high dielectric constant, a technique for reducing antenna size is developed by a wavelength-reducing effect of the dielectric. However, there arise the new problems of a cost increase due to use of the dielectric having a high dielectric constant, and a dimension increase in a thickness direction of the dielectric for maximally deriving wavelength-reducing effect of the dielectric.